This proposal seeks to examine the neurophysiological mechanisms and anatomical connections underlying the control and activation of coordinated body movements. This study is specifically concerned with the functioning of certain reticulospinal neurons and their role as a command system. Little is known about the functional organization of command systems in vertebrates, though they are one of the basic ways for controlling movements in lower animals. The proposed research will examine this issue by studying a model, the neural network that triggers a complex escape response involving a global coordination of the body musculature in teleost fish. We have already identified and studied one prominent cell, the Mauthner neuron, important in this behavioral response. The objectives of the proposed work are to use physiological and anatomical methods to identify the other major neurons important in the escape response. Once these cells are identified, we will study their characteristics and relationship to the Mauthner cell. The long term goal of these studies is to gain insights from this model system into the general mechanisms by which locomotor patterns are initiated and organized by the brain.